The present invention relates to an improvement in a dimersolxe2x80x94difasol plant as described in French patent application FR-B-2 765 573, hereby incorporated by reference, which contains practical details regarding carrying out the process.
In this case, the dimersol is the first step; the difasol process is the second step.
The olefin transformation field has been studied in depth and has formed the subject matter of many patents. Particularly advantageous processes are those that can produce long chain oligomers. Depending on the number of carbon atoms in the chain, such oligomers have applications in chemistry, in petrochemistry, or they form part of the composition of gasoline. In the present invention, depending on the case, the reactions of interest will be olefin dimerisations, co-dimerisations or oligomerisations.
The present invention employs a sequence of processes to carry out, in two steps, olefin dimerisation, co-dimerisation or oligomerisation; in the remainder of this text, the term xe2x80x9coligomerisationxe2x80x9d will cover these three types of reactions.
The first catalytic oligomerisation step of the process of the invention is homogeneous liquid phase catalysis, or heterogeneous catalysis using a solid catalyst. The type of catalyst and the catalyst are selected as a function of the olefin or olefins to be treated and of the product or products to be obtained in the majority. In the case of homogeneous liquid phase catalysis, the catalytic composition is as follows: the catalyst is a nickel compound or a mixture of nickel compounds, the co-catalyst is an alkyl aluminium compound or a mixture of alkyl aluminium compounds or an aluminium halogenoalkyl compound or a mixture of aluminium halogenoalkyl compounds or a halogenoacetic acid or a mixture of halogenoacetic acids and the optional additive to the catalyst can be a compound with an acidic nature, the anion corresponding to this acid, a carboxylic acid ester, an epoxy compound or a phosphine. The catalysts, co-catalysts and optional additives are introduced into a reactor with an internal temperature of about xe2x88x9240xc2x0 C. to +100xc2x0 C., the pressure is such that the reactants are at least partially, preferably mainly in the liquid phase, and the stirring conditions are the conditions necessary to convert at least a portion of the feed. Energetic mechanical stirring is applied to obtain a maximum degree of conversion to oligomers. After this first reaction step, it is optionally possible to isolate the oligomers obtained and/or inhibit the catalyst and/or wash the effluent.
The second step of the process of the invention, the xe2x80x9cdifasolxe2x80x9d process, is an oligomerisation in a liquidxe2x80x94liquid two-phase medium. The reaction medium is a medium with an ionic nature that is not, or is only slightly, miscible with the organic phase containing at least one catalyst that is a nickel complex or a mixture of nickel complexes and possibly at least one additive to the catalyst. The polar phase can also be an ionic medium that is not miscible with the organic phase containing no catalyst, the catalyst for the liquidxe2x80x94liquid two-phase medium oligomerisation reaction is then the catalyst used in the first step (in this case, the first step is a homogeneous catalyst). The catalyst is then introduced into the reactor with the effluent leaving the reactor from the first step.
The medium with the ionic nature comprises at least one salt with formula Q+Axe2x88x92, in which Q+ is a quaternary ammonium or phosphonium cation or a mixture of the two, or a lithium cation, and Axe2x88x92 is a co-ordinating or non co-ordinating anion selected from the group formed by halogenoaluminates, organohalogenoaluminates, organogallates, organohalogenogallates or a mixture of at least two of such compounds.
For this second step, after injecting the feed to be treated, a two-phase medium is obtained which has to be stirred vigorously to ensure good contact between the two phases, this contact being necessary to obtain a good range of conversion into oligomers. In one implementation that can produce good yields, stirring is partially provided by recycling a mixture of the two reaction liquids: the emulsion contained in the reactor is continuously withdrawn and decanted. After decanting, two phases are obtained: an organic supernatant phase is isolated then cooled using a heat exchanger. This cooling can keep the temperature inside the reactor constant and can prevent the catalyst from being damaged by continuous monitoring. A quantity of fresh polar phase, equal to the quantity of polar phase withdrawn and decanted, is injected into the reactor.
After catalysis, for example liquidxe2x80x94liquid two phase catalysis, the effluent from the reactor outlet is washed using a basic solution then water, the oligomers obtained are isolated. This wash can optionally be common with washing of the oligomers produced during the first step, if the latter is carried out.
The cut to be treated containing at least one olefin (Cn) is introduced into a reaction zone where in a first step it undergoes catalytic oligomerisation, either of the homogeneous type carried out in the liquid phase, or of the heterogeneous type carried out with a solid support. The effluent produced is sent to a heat exchanger traversed by a cold liquid. The effluent is thus cooled before being sent to a second reaction zone where it undergoes catalytic oligomerisation in a liquidxe2x80x94liquid two-phase medium. The invention is characterized in that at the inlet to this second reaction zone, at least one C3, C4 or C5, ethylenic hydrocarbon is added. After the reaction, the effluent is directed to a washing zone. After washing, the hydrocarbon fraction is sent to a separator. The fraction containing unreacted olefins (Cn) is separated from the fraction of oligomers produced, this fraction Cn is evacuated from the apparatus. If a mixture of oligomers is obtained after the reaction, this latter fraction is sent to a zone in which it undergoes a second separation step to isolate the desired products from the C(2n+1)+mixture.
It is also possible to envisage, at the outlet from the second reaction zone, the separation string xe2x80x9cNH3+NaCH+H2Oxe2x80x9d before final separation of the desired products from the unconverted products.